Dynamic Drop Test to Be Used for Rock Anchor Testing

Dynamic Drop Test System

A new ASTM standard, D7401, Test Methods for Laboratory Determination of Rock Anchor Capacities by Pull and Drop Tests, is the result of requests to standardize a test to determine dynamic rock anchor capacity that is used internationally in the mining industry. The new test method was developed by Subcommittee D18.12 on Rock Mechanics, part of ASTM International Committee D18 on Soil and Rock.

Most underground excavations require ground support to maintain excavation stability and to ensure a safe environment for personnel and equipment. An appropriate ground support design matches the characteristics of support elements with the anticipated rock mass behavior over time. Engineers and technicians must consider unpredictable dynamic conditions, such as a rock burst.

Increasingly, dynamic capabilities are becoming key design parameters for the selection of yielding ground rock anchor support elements in highly stressed, burst-prone or high deformation environments. Ideally, the engineer or technician needs to know the influence of parameters such as hole diameter, environmental factor, corrosion, resin or cement quality control tolerances for dynamic support application and to determine whether these factors and parameters differ from the static ones. The situation is further complicated as new dynamic yielding rock anchor products arrive on the market to meet the requirements of the mining industry.

In D7401, dynamic loading of a ground support rock anchor is simulated by dropping a mass over a selected distance, onto the rock anchor installed in a simulated borehole. The rock anchor’s behavior under dynamic loading is then analyzed in terms of loads, displacements and energy dissipated. This allows for comparative analysis of different rock anchor supports as well as detailed analysis of the factors affecting the overall quality and performance of the ground support. These are the factors affecting the overall performance of ground support systems that individual mine sites must consider when selecting the most appropriate ground support to ensure the safety of the workforce.

Government agencies, mining companies and mining equipment manufacturers, academia and consulting firms engaged in laboratory testing of rock are among the most likely users of D7401. Subcommittee D18.12 welcomes feedback from interested users that may be used in future revisions of the standard.